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14 Mar 2009, 22:48

(This passage is excerpted from an article that was published in 1982.)

Warm-blooded animals have elaborate physiological controls to maintain constant body temperature (in humans, 37℃). Why then during sickness should temperature rise, apparently increasing stress on the infected organism? It has long been known that the level of serum iron in animals falls during infection. Garibaldi first suggested a relationship between fever and iron. He found that microbial synthesis of siderophores—substances that bind iron—in bacteria of the genus Salmonella declined at environmental temperatures above 37℃ and stopped at 40.3℃. Thus, fever would make it more difficult for an infecting bacterium to acquire iron and thus to multiply. Cold-blooded animals were used to test this hypothesis because their body temperature can be controlled in the laboratory. Kluger reported that of iguanas infected with the potentially lethal bacterium A. hydrophilia, more survived at temperatures of 42℃ than at 37℃, even though healthy animals prefer the lower temperature. When animals at 42℃ were injected with an iron solution, however, mortality rates increased significantly. Research to determine whether similar phenomena occur in warm-blooded animals is sorely needed.

24. The passage is primarily concerned with attempts to determine(A) the role of siderophores in the synthesis of serum iron(B) new treatments for infections that are caused by A. hydrophilia(C) the function of fever in warm-blooded animals(D) the mechanisms that ensure constant body temperature(E) iron utilization in cold-blooded animals

25. According to the passage, Garibaldi determined which of the following?(A) That serum iron is produced through microbial synthesis.(B) That microbial synthesis of siderophores in warm-blooded animals is more efficient at higher temperatures.(C) That only iron bound to other substances can be used by bacteria.(D) That there is a relationship between the synthesis of siderophores in bacteria of the genus Salmonella and environmental temperature.(E) That bacteria of the genus Salmonella require iron as a nutrient.

26. Which of the following can be inferred about warm-blooded animals solely on the basis of information in the passage?(A) The body temperatures of warm-blooded animals cannot be easily controlled in the laboratory.(B) Warm-blooded animals require more iron in periods of stress than they do at other times.(C) Warm-blooded animals are more comfortable at an environmental temperature of 37℃ than they are at a temperature of 42℃.(D) In warm-blooded animals, bacteria are responsible for the production of siderophores, which, in turn, make iron available to the animal.(E) In warm-blooded animals, infections that lead to fever are usually traceable to bacteria.

27. If it were to be determined that “similar phenomena occur in warm-blooded animals” (lines 21-22), which of the following, assuming each is possible, is likely to be the most effective treatment for warm-blooded animals with bacterial infections?(A) Administering a medication that lowers the animals’ body temperature(B) Injecting the animals with an iron solution(C) Administering a medication that makes serum iron unavailable to bacteria(D) Providing the animals with reduced-iron diets(E) Keeping the animals in an environment with temperatures higher than 37℃

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